The present invention relates to refrigeration climate control systems, the systems that either absorb heat from indoor air and reject it to ambient or deliver heat absorbed from ambient to indoor air. Those systems include residential and commercial heat pumps and air conditioners. Invention also relates to refrigeration systems with air circulating in an enclosed volume. Those systems include, for example, dehumidifiers and heat pumps for clothing dryers.
Air conditioners/heat pumps, and dehumidifiers operate conventional refrigeration cycle (FIG. 2) and in a cooling mode extract heat from indoor air and condense moisture from this air, delivering extracted heat along with heat from the compressor to ambient. For air conditioners and heat pumps, ambient is normally outdoor air or other outdoor media. For dehumidifiers ambient is same indoor air. In cooling mode heat pumps and air conditioners reduce temperature and humidity of the indoor air to a comfortable level while dehumidifiers reduce humidity increasing indoor air temperature. For air conditioners and heat pumps, a set of indoor air temperature and airflow rate through the evaporator together with a given indoor air exchange rate and conditions of outdoor air will also define indoor air humidity. When air conditioner/heat pump operates in the cooling mode, average indoor air relative humidity (RH) can stay in comfortable level of around 35-50%. However, even with average indoor air humidity of 50% or below RH of chilled air leaving evaporator may reach 90-95%. Air with such high humidity carries small water drops that accumulate on air duct surfaces or even on the walls inside of a building that may result in mold and allergies. Reduction in airflow through the indoor heat exchanger (evaporator), or reduction in the evaporator dimensions, or heating air after the evaporator with an additional heater or with a condensing coil may reduce indoor air humidity, but with considerable up to 15-20% reduction in cooling capacity and efficiency of air conditioning. Besides, during summer time in many places with high outside air temperature and humidity and with increased indoor air exchange (i.e. old buildings, open windows or doors) average indoor air relative humidity may rise far above 50% and even 70%. Thus, the danger of water accumulations in air ducts and on the walls can be even higher and will require adding to leaving evaporator air considerable heat.
Climate controlling heat pumps operating in a heating mode extract heat from outside air and deliver this heat together with heat from compressor to the indoor heat exchanger while heat pumps in dryers reheat circulating air. A fan blowing air through the warm heat exchanger coil transfers heat to air. Concerning climate control systems in warm regions such as, for example, Florida, most of the time heat pumps provide sufficient indoor air temperatures through wintertime. However, in colder regions, heat pumps often require additional gas or resistance heaters, and generally are not efficient with low outdoor temperatures.
One solution to improve heat pump operations in the heating and cooling modes, also as air conditioner in cooling mode has been presented in U.S. Pat. No. 5,689,962. The patent offers schematics in which an indoor heat exchanger is divided in two parts. In the heating mode the first part becomes a condenser the second is a subcooler. In the cooling mode the first part of the heat exchanger is a subcooler and the second is an evaporator. The design problems are how to properly operate “subcooler” and what way to split indoor heat exchanger into two parts. If the parts are equal or approximately equal, the heat pump will operate inefficiently in both modes. If one part is much larger than another, heat pump is extremely inefficient in a mode where subcooler is larger than the evaporator or condenser. Concerning the method for dehumidifying and cooling air, there is only one refrigerant expansion before the subcooler, thus the subcooler works as a part of the evaporator. Lack of any expansion in the method for heating air makes the system not operable.
More specifically, U.S. Pat. Nos. 6,212,892 and 6,595,012 offer a refrigeration cycle with two expansions (see FIG. 3) for a heat pump. The cycle first has been introduced by the author of the present invention in an application for U.S. Pat. No. 5,755,104 to improve efficiency of refrigeration system with a thermal storage. Further, the cycle with cascade expansions was used in U.S. Pat. Nos. 6,212,892 and 6,595,012. As in the initial patent in these patents the cycle with two consecutive expansions has been offered exclusively for air conditioner or heat pump in cooling indoor air modes but not for the heating mode of a heat pump. Both patents specify two different cooling modes: conventional and with enhanced dehumidification. In dehumidification mode that operates the cycle of FIG. 3 both patents consider that auxiliary coil works as a subcooler. It implies that independently on expansion in the first expansion device the system would operate with efficient subcooling. This is an incorrect assumption. Insufficient subcooling may greatly affect efficiency of the system. For proper subcooling, refrigerant charge of the system is supposed to be higher than without subcooling. However, increased refrigerant charge will be collected in an accumulator or, in a worse case, excessive liquid refrigerant may reach the compressor, causing liquid slugs. Thus, practically it's very difficult to get condensing and deep subcooling in a heat transfer coil with a conventional geometry. As a consequence, offered in these patents design may increase condensing temperature and considerably reduce efficiency of the system. Also, as in U.S. Pat. No. 5,689,962, U.S. Pat. Nos. 6,212,892 and 6,595,012 don't specify dimensions of the auxiliary coil. Besides, U.S. Pat. Nos. 6,212,892 and 6,595,012 offer a second reversing valve turning on and off to alternate the conventional cooling mode with the mode with enhanced dehumidification. This brings additional installation, operating, and maintenance expenses.